* Total Station Topcon GTS-235N

Instrument Setup
1. Make sure tripod legs are securely tightened and well set into ground surface, and that upper
mounting plate is as level as possible before mounting instrument. On sloping ground, have one
leg upslope. Carefully mount the instrument with the screw from the tripod. If you are going to
occupy a benchmark, position the instrument as near as possible over the benchmark; you
should use the plumbob to get it close ( within a centimeter or so) – you' ll be able to get it closer
after leveling using the laser plummet. You should remove the plumbob before continuing.
2. Identify the components you need to use:
a) The tribrach at the base, which contains
three leveling screws and a circular bubble
for coarse leveling. There' s also a lock
which you can undo to release the tribrach,
but you won' t need to do this.
b) Two identical LCD display units with:
• Power
• Menu
• Escape
• Enter
• Star
• NEZ coordinate mode
• Horizontal distance mode
• Angular measurement mode
• left-right and up-down
• Function
buttons used for menu choices.
c) A sighting telescope with eyepiece and lens
sides. Focus is the outermost brown circle, with
the cross-hair focus the tiny black ring around
the eyepiece. Above the telescope is a rough
sighting collimator with a triangle visible inside.
d) Horizontal and vertical control knobs: larger
motion clamps which are loosened for free movement and coarse adjustment, and
tightened for fine adjustments with the tangent screw, mounted on the motion clamp.
Located beside and above one of the display units and to the lower left of the telescope
lens. If it' s on the eyepiece side, loosen the vertical motion clamp and rotate the
telescope 180° to get the lens on the clamp side – this is called the direct reading, and is
required for the data collector to work.
e) Plate bubble level, mounted above one of the displays.
f) A battery in the post to the left of the vertical control. The battery can be released with a
button on the top.
g) There are other parts like the laser plummet you shouldn' t mess with, and signal and
power ports which you' ll use later.
Check the battery level. You need to charge it before using it.
3. Coarse-level the instrument using the bubble level on the tribrach. Tip: Start by positioning
yourself in line with one of the adjustment knobs ( C) , with the other two knobs ( A & B)
forming a perpendicular ( see figure below) . Then simultaneously adjust A & B to tilt the
instrument to the left or right; always turn them together either in or out from your
perspective – you' ll be turning the knobs in opposite directions, but think in or out. Once
centered left to right, use the third knob C independently to center the bubble front to back.
You may have to do the left-right centering again, etc. You can also do this with one knob
( C) towards you.
4. Fine-level the instrument. Use the 30 " ( 30 seconds of angle) plate level above one of the
LCD displays to do a fine adjustment. You' ll use the same adjustment knobs, but you will
need to ( loosen the horizontal motion clamp and) rotate the instrument parallel to the leftright
axis, then parallel to the front-back axis, to do each of those adjustments. You' ll notice
that the adjustment is very sensitive, requiring tiny movements, and the bubble moves slowly
to its stable reading – wait 5 seconds for it to adjust each time before you adjust any more.
Check the level in all four directions by rotating 90° each time. If your tripod is not mounted
on stable ground, you' ll never get it leveled.
5. If occupying a benchmark, reposition over the benchmark using the laser plummet.
Note: One method that may make it easier to position over the benchmark is to remove the
instrument from the tribrach while positioning the tribrach over the point. Since it' s locked,
you' ll need to unlock it by first using the small screwdriver in the toolkit to undo the safety
on the lock, then unlocking and removing the instrument ( carefully)
a) Power up the display. Wait a few seconds for the initial and contrast settings to display,
followed by the normal angle mode display ( V and HR values displayed) .
b) Press the star key to get to the star menu, and select the laser plummet with F4. The
laser plummet will then illuminate a visible red dot on the ground.
c) Loosen the tripod screw to position the dot on the benchmark; then tighten the screw.
d) Turn off the laser plummet to save power.
6. Extra-fine leveling using the tilt sensor. You can use the internal tilt sensor to get it leveled
even better. ( If not already on, power the instrument up and wait for the normal angle mode
display.) Use the Star menu, then F2 to select the tilt sensor. Initially the X-On ( F1) mode is
on, which you use to make tiny adjustments to the front-back tilt – the goal is to get it within
5 " of 0. Then select XY-On ( F2) to adjust the right-left. From here you can also make more
front-back adjustments. F4 lets you check the laser plummet if you want.